1 Answer
1

Looking in the manual (bottom of page 75):
"There’s one downside to buildings: most of them cost gold to maintain. The price depends
upon the building in question, and can range from 1 to 10 per turn. The gold is deducted
from your treasury each turn. See “Gold” on page 103 for more details on maintenance." (Page 103 does not provide any more relevant information on this)

So there does not seem to be additional maintenance costs for cities that are further away.
But:
(1) roads costs maintenance now so a road to a city further away will cost more
(2) to get a trade route (which gives additional income) you need to connect a city to your capital which can be more difficult the further away it is.

Harbors will let you establish a trade route without keeping up a road - so long as you have coastal cities, don't bother with an expensive road!
–
JeffreyOct 13 '10 at 12:39

But roads do not cost maintenance if they are outside your borders, so a road connecting two cities across a vast empty continent don't cost any more than if their borders connected.
–
GoatRiderOct 14 '10 at 0:29